How It Works

Does Earth spin slower now than it used to?

Thanks to thousands of years’ worth of observations recorded by astronomers, we know that the Earth’s rotation has slowed down over the years. The rotation – or the length of a day – can vary by as much as a millionth of a second. It hasn’t been a steady decline, but over that period of time the decline has been up to 25 millionths of a second per year. This is all due to the way that the moon interacts with the tidal bulges on our planet, but there’s also a relationship between the weather and the Earth’s rotation.

Answered by Shanna Freeman, How It Works contributor.